Atomic Structure History Chem: Objective 2b-d

Activity Research topic using books supplied. Write down your information found. Be able to present at the end of class today. Must have a visual of some kind Create a visual/act it out/etc.

Assignments Purple: John Dalton and his contribution to the atom Green and Yellow: J.J. Thomson and his contribution to the atom Pink and Orange: Rutherford and his contribution to the atom Blue: Explain The Law of Conservation of Matter; Law of Definite Proportions; Law of Multiple Proportions

Atom Beginings Democritus Aristotle Greek philosopher “Atomos” = uncut/indivisible Did not have evidence Aristotle Believed all matter was made up of 4 elements: Earth, Air, Fire, Water

The Atomic Theory John Dalton School teacher Used experimental evidence – lab work Dalton proposed a 5 point theory – did not fit all observations Proposed 3 laws: (at the time were not laws) Conservation of Mass Definite Proportions Multiple Proportions

Law Conservation of Mass Matter can neither be created nor destroyed.

Law of Definite Proportions Ex: (Table Salt) NaCl The same elements in exactly the same proportions by mass regardless of the size of the sample or sources of the compound. By mass always consists 39.34% Na; 60.66% Cl.

Law of Multiple Proportions Balanced equations

Dalton’s Atomic Theory All matter is composed of extremely small particles called atoms. Atoms of given element are identical in size, mass, and other properties Atoms cannot be subdivided, created, or destroyed Atoms of different elements combine in simple whole-number ratios to form chemical compounds In chemical reactions, atoms are combined, separated, or rearranged.

Discovery of Electrons J.J. Thomson Did experiments using cathode-rays Opposite attract/Like repel Discovered atoms were made of small negatively charged particles = electrons Discovered the atom is NEUTRAL.

Cathode Ray Vacuum tube Two metal plates at each end Cathode plate(-) Anode plate (+) Magnets deflected charges(glowing beam) The beam was made of NEGATIVE charges ELECTRONS were discovered Led to the plum pudding model (choc chip cookie) Explained the atom was NEUTRAL!!

Discovery of Nucleus Ernest Rutherford Shot alpha-particles at thin, gold foil. Particles deflected Alpha-particle: 2protons, 2 neutrons, (+) charge Force of alpha-particles being returned was due to a densely packed bundle of matter with (+) charge Discovered the NUCLEUS Dense, (+), Accounts for mass of atom, not volume

Gold-Foil Experiment

Gold-Foil Experiment (zoom)

Rutherford Model

Activity From the Notes Make 5 test questions Each person make 3 flash cards – don’t show others

End of Section 1

What is an atom? Atom: the smallest unit of matter that retains the identity of the substance 3 subatomic particles Proton (+) Electrons (-) Neutral (0) 18

Atomic Structure Atoms are composed of 2 regions: Nucleus: the center of the atom that contains the mass of the atom Electron cloud: region that surrounds the nucleus that contains most of the space in the atom Nucleus Electron Cloud 19

Atomic Structure The Nucleus The nucleus contains 2 of the 3 subatomic particles: Protons: positively charged subatomic particles Neutrons: neutrally charged subatomic particles 20

Atomic Structure The Electron Cloud The 3rd subatomic particle resides outside of the nucleus in the electron cloud Electron: the subatomic particle with a negative charge and relatively no mass 21

Atomic Structure Each element has its own atomic number Atomic number: the number of protons Elements are neutral The number of protons are = the number of electrons Electric force – holds the atom together Electric force between protons and electrons Opposites attract

Atomic Number vs. Mass Number Atomic Number : # of protons The ATOM’S number Mass Number: # of protons AND # of neutrons Sums up the Nucleus

Isotope Atoms with same number of protons, different number of neutrons. Isotopes vary in mass Isotopes are distinguished by their # of neutrons

Isotopes Some isotopes are more abundant than others. Unstable isotopes are called radioisotopes They emit radiation and decay into other isotopes Decay until stable Decay at a fixed rate

Isotopes Number of neutrons can be found: Mass Number (Nucleus) – Atomic Number (Protons)

End of Section 2

Modern Atomic Theory The QUANTUM Model

Electron Orbital/Configuration Section 3

Atomic Model All models are proposed theories NO Exact model Bohrs Quantum model NO Exact model Scientist’s experiments Dalton Rutherford Thomson

Atoms 2 Regions Nucleus Electron cloud holds what? Protons (+) Neutrons (0) Electron cloud Electrons (-)

Bohr Model Niels Bohr proposed this model: All of the protons and the neutrons The 3rd ring can hold up to 18 e- The 1st ring can hold up to 2 e- The 4th ring and any after can hold up to 32 e- The 2nd ring can hold up to 8 e-

Bohr Model Orbits: paths electrons follow as they circle nucleus aka: atomic energy levels Orbitals: 3D region around nucleus that indicates probable location of e- definite/fixed energy Closer to nucleus = lower energy Further from nucleus = higher energy

Bohr Model - Orbital Energy Ladder rung

S-Orbital (2e-) Only ONE “s” orbital per enery level

P-Orbitals (6e-)

P-Orbitals-Another look:

D-Orbitals (10e-)

Aufbau Principle States: e- occupies the lowest energy level that can receive it. 1s=lowest energy level 2s=next lowest 2p… and so on

Pauli-exclusion Principle States: no e- in same atom can have same set of 4 quantum #’s Opposite spins No more than two electrons per orbital

Pauli-exclusion Principle

Hund’s Rule Orbitals of equal energy each occupied by 1 e- and all e- in singly occupied orbitals must have same spin. One e- will enter each of the 3 p orbitals in the main energy level before a 2nd e- enters any of them. Example next slide

Energy Level Charts

Hund’s Rule Each orbital must have one e- before another may have a second e-

Quantum Model Principal quantum #: Symbol = “n” Indicates the main energy level occupied by e- n , e- energy and distance from nucleus Total # of orbitals existing in a given energy level = n2 EL 1 = 2 orbitals, EL 2 = 4 orbitals, EL 3 = 9 orbitals

PAUSE Configure Your Electrons WORKSHEET

Practice Lithium At#=3 ___ ___ ___ ___ ___ 1s 2s 2px 2py 2pz Lithium At#=3 ___ ___ ___ ___ ___ Beryllium At#=4 ___ ___ ___ ___ ___ Boron At#=5 ___ ___ ___ ___ ___ Carbon At#=6 ___ ___ ___ ___ ___

Practice Nitrogen At#=7 ___ ___ ___ ___ ___ 1s 2s 2px 2py 2pz Nitrogen At#=7 ___ ___ ___ ___ ___ 1s22s22p3 Oxygen At#=8 ___ ___ ___ ___ ___ 1s22s22p4 Fluorine At#=9 ___ ___ ___ ___ ___ 1s22s22p5 Neon At#=10 ___ ___ ___ ___ ___ 1s22s22p6

Practice Phosphorus Sodium Atomic # = 15 1s22s22p63s23p3 Atomic # = 11

Animation http://www.quimica3d.com/VIDEOS/ORBITALS/en-18.html